Lng ship

ABSTRACT

To obtain an economical hull structure by employing an independent prismatic tank having a large tank volume with respect to a ship size and reducing material cost. 
     Provided is a LNG ship having a structure in which a substantially prismatic tank is installed inside a hold while not being integrated with a hull structure material, wherein a tank bottom surface is provided with inclined surfaces formed at the left and right sides of a center line direction of the ship as a boundary so that each angle intersecting a horizontal line becomes equal to or smaller than 4.0°, and support bodies integrated with the hull structure material are arranged so as to correspond to the inclined surfaces and the tank is put on the support bodies.

TECHNICAL FIELD

The present invention relates to a liquefied natural gas (LNG) ship.

BACKGROUND ART

It has been increasing LNG demand as clean energy every year since the amount of exhausted nitrogen oxides or sulfurous acid gas in combustion is small. The LNG is liquefaction material obtained by cooling a natural gas to about −162° C. Then, a tank of a LNG carrier transporting the LNG on the sea has a structure in which a cryogenic material is used so as to withstand a wide temperature change and thermal shrinkage and thermal stress caused by a temperature difference are taken into consideration. Further, since the LNG carrier is used to transport a large amount of LNG at a high speed, the LNG carrier generally has a speed of about 20 knots, and its capacity exceeding 200,000 m³ is now planned due to the tendency of an increase in size of a hull.

In an existing LNG carrier, a LNG tank mounted thereon is generally divided into two types. One is a moss spherical tank type and the other is a membrane type (for example, see U.S. Pat. No. 5,697,312 and U.S. Pat. No. 7,137,345).

In the moss spherical tank type, a spherical tank made of aluminum alloy is fixed into a hold through a skirt-shaped support structure extending downward from the equatorial portion thereof. In the tank, both the weight of the liquid cargo loaded therein and the dynamic force acting on the liquid cargo due to the rolling of ship are directly put on the tank itself, and are transmitted to the hull through the skirt. Of course, a heat insulating material of the tank is provided on the outer surface of the tank.

Meanwhile, in the membrane type tank, a heat insulating material is provided inside a double hull structure of a hull and a top surface thereof is liquid-tightly covered by a membrane. In this type tank, the liquid pressure of LNG is transmitted to the hull structure through the heat insulating material. As the membrane, stainless steel or nickel alloy (invar) having a small thermal expansion coefficient is used.

Incidentally, since the hold is formed in a substantially box shape, a useless space is inevitably formed around the spherical tank when the moss spherical tank is applied in the hold. For this reason, the moss spherical tank has a disadvantage in that the tank volume is small compared with the size of the hull of both types.

Meanwhile, since the membrane type tank can be made in a shape along the hold, a large tank space is obtained, and hence volumetric efficiency is satisfactory. On the contrary, when the membrane type tank encounters heavy weather in a half load condition, a sloshing phenomenon occurs in which a large pressure is applied (attacked) to the inner wall of the tank due to the harmony of the shaking of the hull and the shaking of the LNG liquid level. That is, the liquid cargo inside the tank is violently ruffled due to the shaking of the hull, and hence the membrane or the heat insulating material is damaged due to the impact. In the spherical tank, since the tank wall is curved, the impact can be smoothly disappeared. Further, since the heat insulating material is provided outside the tank, the sloshing substantially does not cause any problem. Accordingly, in the membrane type tank, there is always a need of full or almost full load condition so that the LNG in the cargo is not ruffled.

The moss type and the membrane type are mainly used in the cargo tank of the LNG ship, but these types have merits and demerits as described above. For the use of the LNG ship, it is important to select the ship type based on the enough consideration of the advantages and disadvantages. Here, an independent prismatic tank is developed as an ideal LNG cargo tank in many ship builders in Japan based on the advantages and disadvantages. As an example thereof, a SPB tank manufactured by IHI Corporation is known.

CITATION LIST Patent Literatures

Patent Literature 1: U.S. Pat. No. 5,697,312

Patent Literature 2: U.S. Pat. No. 7,137,345

SUMMARY OF INVENTION Technical Problem

Unlike the spherical tank, the independent prismatic tank is of an ideal type without any disadvantage in which the tank volume is small compared with the size of the hull of both types.

However, the material of the used plate is limited to a material in which a strength property is exhibited in a cryogenic region, and stainless steel and aluminum are mainly used as the material. For this reason, the independent prismatic tank cannot compete with the moss type and the membrane type from the viewpoint of building cost, and hence only several ships are built.

The LNG is a liquid, and the behavior of the free surface inside the tank causes a large influence. Particularly, the membrane type should avoid the sloshing of the liquid level in the tank of the LNG ship caused by waves due to the tank structure.

An object of the invention is to obtain an economical hull structure by employing an independent prismatic tank having a large tank volume with respect to a ship size and reducing material cost.

Another object of the invention is to obtain a hull structure capable of accurately handling sloshing in a tank liquid level.

The other objects will be proved by the following description.

Solution to Problem

The invention solves the above-described problems as below.

<Invention of Claim 1>

A LNG ship having a structure in which a substantially prismatic tank is installed inside a hold while not being integrated with a hull structure material,

wherein a tank bottom surface is provided with inclined surfaces formed at the left and right sides of a center line direction of the ship as a boundary so that each angle intersecting a horizontal line becomes equal to or smaller than 4.0°, and

support bodies integrated with the hull structure material are arranged so as to correspond to the inclined surfaces and the tank is put on the support bodies.

(Operation and Effect)

In the structure in which the tank is installed inside the hold while not being integrated with the hull structure (for example, the double hull structure) material (without any welding structure), there is an economical advantage in that a high-cost material is not needed. Further, since the tank has a substantially prismatic shape, the volumetric efficiency of the tank is larger than that of the spherical tank.

Meanwhile, the tank bottom surface is provided with the inclined surfaces formed at the left and right sides of the center line direction of the ship as the boundary so that each angle intersecting the horizontal line becomes equal to or smaller than about 4.0°, the support bodies integrated with the hull structure material are arranged so as to correspond to at least the inclined surfaces, and the tank is put on the support bodies.

There is a possibility that the sideslip of the tank may occur with the thermal deformation of the hull caused by a change in LNG amount inside the tank and the like. The thermal deformation sideslip is suppressed or prevented by friction resistance between the tank bottom surface and the support bodies having inclined top surfaces.

It is possible to simply select a tank structure in accordance with a structure material of an oil tanker or a LPG tanker. Precisely, unlike the membrane type, it is unnecessary to use a particular structure for protection against sloshing phenomenon. Thus, economic efficiency is improved in the selection of the material and the structure of the tank.

<Invention of Claim 2>

The LNG ship according to claim 1, wherein a flat surface is formed at a center portion of the tank bottom surface, a receiving body integrated with the hull structure material is provided so as to correspond to the flat surface, and the flat surface is installed on the receiving body.

(Operation and Effect)

Although the flat surface may not be provided in the tank bottom surface, if the flat surface of the tank is installed on the receiving body and the main load of the tank is supported by the receiving body, there is an advantage in strength design of the tank.

<Invention of Claim 3>

The LNG ship according to claim 1 or 2, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions separated from each other in a ship width direction.

(Operation and Effect)

When the support bodies are arranged at the left and right sides at the plurality of positions separated from each other in the ship width direction, the sideslip of the tank occurs smoothly and the weight decreases.

<Invention of Claim 4>

The LNG ship according to claim 1 or 2, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions separated from each other in a ship width direction and are provided along a ship longitudinal direction.

(Operation and Effect)

When the support bodies are arranged along the ship longitudinal direction, the tank can be stably supported.

<Invention of Claim 5>

The LNG ship according to claim 1 or 2, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions in a zigzag pattern.

(Operation and Effect)

The support bodies can be arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at the plurality of positions in the zigzag pattern.

<Invention of Claim 6>

The LNG ship according to claim 1, wherein a key portion is integrally formed with a center upper portion of the tank in a protruding manner and anchor point chocks are provided in the hull structure material so as to be located at front and rear sides in the center line direction of the ship corresponding to the key portion.

(Operation and Effect)

In order to set the center upper portion of the tank as a thermal deformation center of the tank for forward and backward direction, the anchor point chock having a width in the ship width direction is provided in the hull so as to suppress the movement of the tank for forward and backward direction as small as possible, and this point is set as the thermal deformation center. Thus, it is possible to minimize stress in a LNG pipe connected between tanks and an expansion joint connected between a tank and a pipe outside of the tank.

<Invention of Claim 7>

The LNG ship according to claim 1, wherein a material of the prismatic tank is selected from aluminum alloy, 9% nickel steel, and stainless steel.

<Invention of Claim 8>

The LNG ship according to claim 1, wherein the LNG ship includes a LNG carrier, FLNG, FSRU, and SRV.

(Operation and Effect)

The term of the “LNG ship” of the invention is widely used as a ship including a LNG carrier, FLNG, FSRU, and SRV.

Advantageous Effects of Invention

As described above, according to the invention, it is possible to obtain the economical hull structure by employing the independent prismatic tank having the large tank volume with respect to the ship size and reducing the material cost.

Further, it is possible to suppress or prevent the sideslip or the lateral movement of the tank caused by the waves by friction resistance between the inclined surfaces of the tank bottom surface and the support bodies having the inclined top surfaces.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a LNG ship.

FIG. 2 is a plane view of the LNG ship.

FIG. 3 is a cross-sectional view of the LNG ship.

FIG. 4 is a view taken along the line 4-4.

FIG. 5 is a partial plane view of another arrangement example of support bodies.

FIG. 6 is a cross-sectional view of another shape example of a tank.

FIG. 7 is a cross-sectional view of still another shape example of a tank.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings.

As illustrated in FIGS. 1 and 2, a LNG tanker has a structure in which a bow area 10, a tank space 12, an engine room 14, and a stern area 16 are connected in this order from the front side, and an accommodation area 18 and a steering room 20 are provided above the engine room. The tank space 12 is divided into a plurality of sections by transfer bulkheads 22. Reference sign 23 denotes a bulkhead provided for the bow area 10.

The invention relates to a LNG ship in which each independent tank 30 having a substantially prismatic shape is installed inside a hold while not being integrated with hull (double hull) structure materials 32 and 33.

Further, the bottom surface of the independent prismatic tank 30 is provided with inclined surfaces 30A provided at the left and right sides of the center line direction of the ship as the boundary so that each angle θ intersecting a horizontal line H becomes equal to or smaller than 4.0°. Then, support bodies 34, 34 . . . integrated with the hull structure material 33 are arranged so as to correspond to the inclined surfaces 30A and 30A, and the tank 30 is put on the support bodies 34, 34 . . . .

Further, a center portion of the bottom surface of the tank 30 is provided with a flat surface 30B. Then, a receiving body 35 integrated with the hull structure material 33 is provided so as to correspond to the flat surface 30B, and the flat surface 30B is installed on the receiving body 35. The support bodies 34, 34 . . . are arranged along a ship longitudinal direction.

In the invention, since a structure is employed in which the tank 30 is provided as the independent prismatic tank and is installed inside the hold while not being integrated with the hull structures (for example, the double hull structures) 32 and 33 (without any welding structure), there is an economical advantage in that a high-cost material is not needed. Further, since the tank 30 has the substantially prismatic shape, the volumetric efficiency of the tank 30 is larger than that of the spherical tank.

The bottom surface of the prismatic tank 30 is provided with the inclined surfaces 30A formed at the left and right sides of the center line direction of the ship as the boundary so that each angle θ intersecting the horizontal line H becomes equal to or smaller than 4.0°, the support bodies 34, 34 . . . integrated with the hull structure material 33 are arranged so as to correspond to the inclined surfaces 30A and 30A, and the tank 30 is put on the support bodies 34, 34 . . . . Thus, there is possibility that sideslip of the tank 30 may occur with thermal deformation of the hull caused by a change in LNG amount inside the tank. This thermal deformation sideslip is suppressed or prevented by friction resistance between the bottom surface 30A of the tank 30 and the support bodies 34 having inclined top surfaces.

The inclination angle θ intersecting the horizontal line H of the bottom surface 30A of the tank 30 is not limited. However, when the inclination angle θ is set to be large, there is a possibility that the liquid cargo amount may decrease and an extreme sideslip may occur. Accordingly, it is desirable that the inclination angle θ be equal to or smaller than 4.0° and be 0.5° to 2.5°.

Meanwhile, it is desirable to employ a structure in which a key portion 40 is integrally formed with a center upper portion of the tank 30 in a protruding manner and anchor point chocks 41 and 41 are provided in the hull structure material so as to be located at the front and rear sides in the center line direction of the ship corresponding to the key portion 40. Thus, it is possible to restrict the thermal deformation sideslip of the tank for forward and back direction.

Although not illustrated in the drawings, a heat insulating material can be provided on the outer surface of the tank 30.

In the above-described example, the support bodies 34, 34 . . . are arranged along the ship longitudinal direction, but can be arranged appropriately. For example, as illustrated in FIG. 5, the support bodies can be arranged in a zigzag pattern.

The “substantially prismatic independent tank” of the invention may be a prismatic shape in the cross-section as a whole, and does not need to be a precise prismatic shape. For example, as illustrated in FIG. 6, it is possible that a tank 30C includes chamfered corners 30 a and round corners 30 b and inclined top surfaces 30 c.

Further, as illustrated in FIG. 7, it is possible that a tank 30D includes a small tank 30 d at an upper portion and a main tank 30 e at a lower portion.

As a material of the tank 30, aluminum alloy, 9% nickel steel, stainless steel, or the like can be used.

The above-described embodiments can be used in combination.

INDUSTRIAL APPLICABILITY

The invention can be applied to a LNG carrier and in addition, the invention can be applied also to a FLNG (LNG-FPSO (Floating Production, Storage and Off-loading system)), FSRU, and SRV, which require handling of sloshing phenomenon in the same manner as the LNG carrier.

In the FLNG (LNG-FPSO), impurities of natural gas from a marine gas field are removed and the natural gas is liquefied to produce LNG so that the LNG is stored on a ship or a barge having a LNG storage capacity. Then, the LNG is shipped off to a LNG ship for carrying the LNG. As compared with a case where a liquefied natural gas plant is constructed on the land, this system has the following advantages: a pipeline from the marine gas field to the land can be reduced; an environmental load can be reduced because development on the coast is not required; and workers can be comparatively easily secured because the LNG-FPSO is constructed in a country or a region different from those in which a gas field is developed and is towed to the site.

The LNG ship of the present invention includes a re-gasification unit and the examples of the re-gasification unit are an FSRU (Floating Storage and Re-gasification Unit) and SRV (Shuttle and Re-gasification Vessel). The FSRU is mounted with a re-gasification unit and fixes a ship having an LNG storage capacity on the sea and receives LNG from the other LNG ship. The natural gas re-gasified by the FSRU is sent out to a pipeline on the land. The SRV does not transfer LNG from the other LNG ship but transports LNG loaded in at a liquefaction base to a demand area, re-gasifies the LNG on the deck, and sends out the re-gasified natural gas to a pipeline on the land.

REFERENCE SIGNS LIST

10: bow area, 12: tank space, 14: engine room, 16: stern area, 18: accommodation area, 20: steering room, 30, 30A to 30D: independent prismatic tank, 30A: inclined surface, 30B: flat surface, 32, 33: hull structure material, 34: support body, 35: receiving body, θ: inclination angle 

1. A LNG ship having a structure in which a substantially prismatic tank is installed inside a hold while not being integrated with a hull structure material, wherein a tank bottom surface is provided with inclined surfaces formed at the left and right sides of a center line direction of the ship as a boundary so that each angle intersecting a horizontal line becomes equal to or smaller than 4.0°, and support bodies integrated with the hull structure material are arranged so as to correspond to the inclined surfaces and the tank is put on the support bodies.
 2. The LNG ship according to claim 1, wherein a flat surface is formed at a center portion of the tank bottom surface, a receiving body integrated with the hull structure material is provided so as to correspond to the flat surface, and the flat surface is installed on the receiving body.
 3. The LNG ship according to claim 1, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions separated from each other in a ship width direction.
 4. The LNG ship according to claim 1, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions separated from each other in a ship width direction and are provided along a ship longitudinal direction.
 5. The LNG ship according to claim 1, wherein the support bodies are arranged at the left and right sides of the center line direction of the ship as the boundary so as to be located at a plurality of positions in a zigzag pattern.
 6. The LNG ship according to claim 1, wherein a key portion is integrally formed with a center upper portion of the tank in a protruding manner and anchor point chocks are provided in the hull structure material so as to be located at front and rear sides in the center line direction of the ship corresponding to the key portion.
 7. The LNG ship according to claim 1, wherein a material of the prismatic tank is selected from aluminum alloy, 9% nickel steel, and stainless steel.
 8. The LNG ship according to claim 1, wherein the LNG ship includes a LNG carrier, FLNG, FSRU, and SRV. 